The tanning of human epidermis by the sun's rays depends greatly upon the complexion of the individual. Persons with a fair complexion may have difficulty in obtaining a tan. Many such persons merely burn, and, thus, they must restrict their exposure to the sun. Despite the problems which may be encountered by some in obtaining a tan, there is a general desire to tan the skin for cosmetic reasons. Unfortunately, this desire can present serious medical problems for some individuals. Notable is the prevalence of skin cancers.
Obviously, where there is a tendency to burn rather than to tan under the sun's rays, it is desirable to screen out those rays. Accordingly, sunscreen compounds are also quite useful. Sunscreen products are based on compounds which absorb ultraviolet radiation in the range of 290-320 nm; therefore, these products prevent burning but do not promote tanning and offer only temporary protection.
In order to satisfy the cosmetic desires of individuals without incurring the undesirable effects of sun rays, there have been made available skin coloring products. Such products are typically based on dihydroxyacetone, which darkens the skin by interacting with the keratin in the stratum corneum. Although darkening can be achieved, a natural color is difficult to produce, and the color is not even and may be selectively removed by washing. Understandably, such products have not achieved market acceptance.
Though tanning of the human skin is motivated largely by cosmetic desires, it is also recognized that tanning, when done without detrimental burning, can have a protective effect on the skin. Thus there exists a need for a preparation to produce a natural-appearing tan which can protect the skin from potentially harmful radiation from the sun.
The commercially-available products for tanning and sunscreening, as noted above, have various limitations which militate against their extensive use. It should also be recognized that it is highly desirable that any compound or means for overcoming these limitations should also be non-mutagenic and non-allergenic since these are highly relevant and desired characteristics for any compound used on the human body.